This invention relates to door operators which move a door between an open position and a closed position and which stop or reverse movement of the door in response to an obstruction that is encountered during movement of the door between the open and closed positions. Specifically, this invention relates to an improved position control apparatus to control the door operator motor when the door approaches the open position and the closed position and relates to improved obstruction detector apparatus to stop or reverse the motor if an obstruction is encountered as the door moves between the open and closed positions.
The prior art includes three broad approaches to provide control for a door operator motor as the door approaches the open position and the closed position. One approach is to place limit switches in the path of movement of the door or the linkage which connects the door to the operator as shown in U.S. Patent 1,215,573. One of the limit switches is actuated as the door approaches the open position and the closed position. When either limit switch is actuated, the motor is de-energized. A second approach is to sense resistance to further movement of the door as the door reaches the limits of the rails which support the door at the open position or the closed position as shown in U.S. Patent 2,883,182. When resistance to further movement is sensed, the motor is deenergized. A combination of these two approaches is found in U.S. Patent 2,568,808 which includes a limit switch to control the motor as the door approaches the open position and a means to sense resistance to further movement as the door reaches the closed position to control the motor. The third approach is a mechanical analog for movement of the door, such as shown in U.S. Patent 1,686,851 which discloses a position control screw that drives a traveling body along a path in contact with strips which are adjustable to set the open and closed positions. When the traveling body is driven out of contact with either of the strips, the motor is de-energized.
In U.S. Patent 1,686,851, as well as more recent prior art, such as U.S. Patent 3,996,697, the position control screw is driven through a mechanical linkage, such as a gear or pulley speed reduction apparatus. The complexity of this apparatus, such as the number of elements, as well as the assembly time, for such position control apparatus renders these door operators relatively expensive. Also in this category is U.S. Patent 3,955,661 which includes a speed reduction ball drive assembly through which the position control screw is driven. Perhaps the most direct prior art approach is shown in U.S. Patent 3,078,407 which includes travel nuts on the drive screw for a door operator. Nevertheless, because no apparent speed reduction is provided between the drive screw and the position control screw in U.S. Patent 3,078,407, since they are one in the same, the travel of the travel nuts must be over a substantial distance or else a portion of the drive screw must be finely threaded so as to require a high quality, high strength material over the entire length of the drive screw which is relatively expensive. Moreover, disconnection of the drive screw from the door operator motor to facilitate packing or shipping would be inconvenient due to difficulty of installation of the door operator because of realignment of the integral position control and drive screw with the associated position control switches. Furthermore, the integral position control and drive screw could be bowed due to misalignment during installation and is subjected to forces which cause bowing during operation. This results in binding of the travel nuts on the finely threaded position control screw portion so as to produce metal dust which fouls or abrades the threads of the travel nuts so that the travel nuts break or wear out.
Safety considerations require that the door operator motor also be de-energized, or reversed, if an obstruction is encountered by the door as the door is moved in either direction between the open and closed positions. The prior art includes various approaches to detect an obstruction, such as a person or automobile, in the path of the door. As a safety precaution, the motor is either stopped or reversed when an obstruction is encountered to prevent injury or damage.
One approach to detect an obstruction is to sense the reaction torque upon the door operator motor by rotation of a rotatably mounted motor casing, such as shown in U.S. Patents 3,764,875 and 3,787,725. See, also, U.S. Patent 2,387,533. The door operator in U.S. Patent 3,764,875 includes a complex mechanical linkage to sense rotation of the motor casing so as to actuate a safety switch if the door hits an obstruction during closing. On the other hand, the door operator in U.S. Patent 3,787,725 includes two safety switches which are provided to sense rotation of the motor casing if the door encounters an obstruction during opening or closing. The complex mechanical linkage or plurality of safety switches in prior art door operators makes them difficult to assemble and expensive.